1. Field of the Invention
The present invention relates to a drive apparatus for a zoom lens barrel.
2. Description of the Related Art
A zoom lens includes at least two movable zooming lens groups which are moved in predetermined directions upon zooming. In a first type of conventional or classical drive mechanism of the zoom lens, which has been used particularly for a single lens reflex camera, in which a focal-shift during zooming is not permitted, the movable zooming lens groups are moved along tracks defined by cam grooves formed on a cam ring so as not to cause a focal-shift. In a second type of known drive mechanism of a zoom lens for compact cameras or digital cameras, in which correct focusing on an object is requested only at the time of shutter releasing while the shift of focus during zooming is accepted, the movable zooming lens groups are moved upon zooming while permitting a focal-shift, and thereafter the movable lens groups are moved to an in-focus position in accordance with set focal length data and set object distance data upon the shutter releasing. In the second type drive mechanism, separate drivers for the two movable lens groups are provided, so that the positions of the lens groups are detected as digital data and controlled thereby. The "zooming" or "zooming operation" refers to both the first type drive mechanism in which the zoom lens groups are moved so as not to cause a focal-shift and the second type drive mechanism in which the zoom lens groups are moved while permitting the shift of focus. It goes without saying that in the type of drive mechanism in which the separate drivers for the two zoom lens groups are provided and the positions of the lens groups are detected as digital values, it is possible to move the zoom lens groups without causing a focal-shift.
The second type drive mechanism for a zoom lens barrel, in which the drivers for the two zoom lens groups are provided, is larger in size and more complicated in construction than the first type drive mechanism in which the zoom lens barrels are moved by the single cam ring.